1. Field of Invention
The present invention pertains to the fields of measurement/control systems. More particularly, this invention relates to a modular system with synchronized timing.
2. Art Background
A wide variety of systems including measurement/control systems commonly include a variety of instruments that provide measurements and apply stimulus. Examples of instruments are numerous and include instruments for measuring physical characteristics such as temperature, pressure, voltage, etc., as well as the instruments for generating stimuli such as heat, mechanical stimuli, chemical stimuli, electrical stimuli, etc.
It is often desirable in a system to provide coordination of the measurements obtained by its instruments and/or the stimuli applied by its instruments. For example, it may be desirable to precisely control the timing of stimuli applied by an instrument and/or accurately record the time at which measurements are obtained by the instrument. In addition, it is often desirable that a system have a modular design in which different types of measurement modules and stimulus modules may be employed.
Prior systems commonly employ modular instruments which usually have an instrument housing that holds a set of modules each of which performs a measurement and/or stimulus function. Typically, the modules in such an instrument housing communicate via an internal bus of the instrument housing. Examples of internal buses include VME, VXI, PXI, PCI, and CPCI. One example of a such a bus implemented with a set of cables is the IEEE 488 standard. Typically, the application of stimuli and/or the measurements obtained by such an instrument are coordinated by transferring commands via its control bus or by using dedicated external trigger wires.
Typically, such an instrument housing accepts up to a maximum number of modules. If a system requires a number of modules that exceeds the maximum for an instrument housing then additional instrument housings must usually be employed. The use of multiple instrument housings usually requires an engineering effort to provide coordination among the modules contained in different instrument housings. Unfortunately, such an engineering effort typically increases the costs associated with using prior systems.
In addition, the modules of prior systems are typically confined to an instrument housing or a relatively short distance from an instrument housing and have transducer connections of limited length. As a consequence, such prior systems are usually not suitable for obtaining coordinated measurements and applying coordinated stimuli at points of a system which are widely dispersed.